I made a what I thought was a carefully balanced spell point system. After playing it for a while, it became obvious that mid-level casters became way too powerful, and I decided to go back to good old memorization.
A word of advice: if you do use spell points, keep the spells with affixed metamagic feats as being x levels higher, and keep the max spell level limit. Otherwise, you'll end up with 5th level wizards casting quickened haste (like I did). And to remember that I thought that +200% spell points for Quicken Spell was too much...